A 41-year-old woman was diagnosed with pre-eclampsia at 35 weeks gestation. She was treated with antihypertensives but, unfortunately, her condition became complicated by severe hyponatraemia. Her sodium levels rapidly dropped to 125 mmol/L. The cause for the hyponatraemia was the syndrome of inappropriate antidiuretic hormone secretion. She was initially managed with fluid restriction, but an emergency caesarean section was necessary in view of fetal distress. Her sodium levels returned to normal within 48 hours of delivery.Pre-eclampsia is rarely associated with hyponatraemia. A low maternal sodium level further increases the mother's risk for seizures during this state. Additionally, the fetal sodium rapidly equilibrates to the mother's and may result in fetal tachycardia, jaundice and polyhdraminios. All these factors may necessitate an emergency fetal delivery.